Solving Subspindle Part-Ejection Problems

When parts fail to eject properly from the subspindle of a four-axis lathe or Swiss screw machine, the result can be hours of downtime and a big bill to repair the damage. If you are plagued by this problem, you will be interested in the Subspindle Part Ejection Device (SPED) made by Zenna Industries.

Article Post: 5/15/2003

Leo Rakowski

Editor

Cutaway views of the collet show SPED in the at-rest position with the spring relaxed and the tip just protruding from the collet opening (left). When the workpiece is transferred from the main spindle to the subspindle collet, it pushes the tip and stem back into the collet, compressing the spring (right). After the back-end machining operations are completed, the collet opens, releasing the workpiece. The spring then relaxes, ejecting the part.

The components are shown assembled. The body is not installed until the tip, stem and spring are inserted in the collet.

Components of the subspindle part-ejection system (from left): the tip, stem, spring and body.

SPED is shown assembled in the collet, ready for installation in the subspindle.

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When parts fail to eject properly from the subspindle of a four-axis lathe or Swiss screw machine, the result can be hours of downtime and a big bill to repair the damage. If you are plagued by this problem, you will be interested in the Subspindle Part Ejection Device (SPED) made by Zenna Industries (Spring Lake Park, Minnesota). SPED replaces the standard ejector rod originally supplied with the machine with a simple assembly that uses spring power to eject the part from the subspindle collet. The system is fast and easy to install, relatively inexpensive and fits most machines that have a subspindle. The manufacturer reports that there are no known instances of SPED having failed to perform satisfactorily.

The device consists of four components: a tip, stem, body and compression spring, all of which fit inside your existing subspindle collet. (See photos.) Assembly is fast and easy. First screw the tip (appropriately sized to the bar size that you are running) into the front end of the stem. Next, slip the compression spring over the back end of the stem and insert the assembly, tip first, into the back of the collet. Apply light oil or grease to the rubber O-rings on the body, and then insert the body into the back of the collet making sure that the back end of the stem passes through the body’s center bore. Finally, insert the collet into the subspindle, and you’re ready for production.

The cutaway views of the collet show how SPED works. In the idle position, the compression spring is in the relaxed (uncompressed) position. It holds the stem in the forward position so that the tip just extends from the collet opening. When the cutoff workpiece is transferred to the subspindle collet for back end machining operations, it pushes against the tip, forcing the stem back into the collet and compressing the spring. (The back end of the stem is free to move back and forth through the center bore in the body at the back of the collet.) When the back end machining operations are completed, the collet opens and the spring returns to its original position, ejecting the part.

Zenna Industries’ Jake Christian notes that damage to the machine and/or tooling caused by failure of parts to properly eject can take a machine out of production for as long as 8 hours. Standard ejector rods have been known to bend and can cost as much as $300 to replace. The device eliminates these problems and the downtime associated with them.

In addition to SPED, the company offers a 16-piece set of tips in fractional sizes up to 0.5 inch to simplify matching popular bar sizes.